1. Field of the Invention
Aspects of the present invention relate to a dye-sensitized solar cell, and more particularly, to a dye-sensitized solar cell with improved photoelectrical conversion efficiency by using a polymer electrolyte.
2. Description of the Related Art
Dye-sensitized solar cells are photoelectrochemical solar cells using photosensitive dye molecules capable of generating electron-holes pairs by absorbing visible rays and an oxide semiconductor electrode that transfers the generated electrons and is formed of titanium oxide.
In a conventional silicon solar cell, the absorption of solar energy and the generation of an electromotive force by the separation of electron-hole pairs occur simultaneously in a silicon semiconductor. Meanwhile, in a dye-sensitized solar cell, the absorption of solar energy and the transfer of charges occur separately. In particular, in the dye-sensitized solar cell, a dye absorbs the solar energy, and a semiconductor electrode transfers the charges.
Such dye-sensitized solar cells have low manufacturing costs, are environmentally friendly, and can be manufactured to be flexible. However, due to low energy conversion efficiency, there is a limit to the practical application of dye-sensitized solar cells.
The energy conversion efficiency of a solar cell is in proportion to the amount of electrons generated by the absorption of solar light. The energy conversion efficiency can be increased by increasing the absorption of solar light, by increasing the absorbed amount of dye to generate more electrons, or by preventing the loss of excited electrons by the recombination with holes.
To increase the absorption of a dye in a unit area, a method of preparing nano-sized oxide semiconductor particles, a method of increasing the reflectivity of a platinum electrode to increase the absorption of solar light, a method of adding micro-sized optical scatterers of semiconductor oxide, etc., have been suggested.
A solar cell presented by Gratzel et al. from Switzerland in 1991 is a representative example of conventional dye-sensitized solar cells. The solar cell presented by Gratzel et al. is a photoelectrochemical solar cell using photosensitive dye molecules and an oxide semiconductor composed of titanium dioxide nanoparticles. The manufacturing costs of the solar cell are lower than silicon solar cells. Currently available dye-sensitized solar cells include a nanoparticle oxide semiconductor cathode, a platinum anode, a dye coated on the cathode, and an oxidation/reduction electrolyte using an organic solvent. In such a conventional dye-sensitized solar cell comprising an electrolyte prepared using an organic solvent, the organic solvent of the electrolyte is likely to volatilize when the external temperature of the solar cell rises due to solar light. Thus, the long-term stability and practicality of the dye-sensitized solar cell deteriorate.
Korean Patent Publication No. 2003-65957 discloses a dye-sensitized solar cell containing polyvinylidene fluoride-containing gel type polymer electrolyte in which the volatility of an electrolyte solvent is reduced to increase the photoelectric conversion efficiency. However, the energy conversion efficiency of the solar cell is lower than when an organic solvent-containing electrolyte is used. Therefore, there is a need to develop a polymer electrolyte with long-term stability and high energy conversion efficiency.